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Behind the Equipment Grounding Conductor

Jul 1, 2000 12:00 PM, By James Stallcup, Sr. and James Stallcup, Jr.

Although it's rather simple component, an equipment-grounding conductor (EGC) serves a vital role in your overall electrical system.

You use an equipment-grounding conductor (EGC) to ground the noncurrent-carrying metal parts of equipment. Its function is to keep your equipment as close as possible to ground potential and provide a safe path for ground-fault current to flow. A properly sized EGC protects circuit elements and equipment and ensures the safety of your personnel from electric shock. Let's take a closer look at installation guidelines.

The NEC allows you to install an EGC in a raceway, cable tray, cable armor, or cable sheath. Per Sec. 250-134(b) and Sec. 300-3(b), the EGC must be contained within the same raceway, cable, or otherwise run with circuit conductors. You size an EGC based on the size of the overcurrent protection device (OCPD) protecting the circuit conductors of the electrical circuit in question.

The sizing and installation of the EGC must conform to the rules of Sec. 250-122 and Table 250-122. Where you have to increase current-carrying conductors in size to compensate for voltage drop, adjust the EGC proportionately to the circular mil area per Sec. 250-122(b) . The NEC also permits you to run a single EGC with multiple circuits in the same raceway per Sec. 250-122(c), as long as you size it based on the largest overcurrent device protecting the conductors in the raceway or cable.

For example, if you route three No. 10, two No. 12 and three No. 14 conductors in the same raceway, you can pull a No. 10 EGC through the raceway to serve as a grounding means for all circuit conductors.

When you install a No. 6 or smaller EGC, the insulation along its entire length must be colored green or green with one or more yellow stripes. You can also use a completely bare EGC under certain conditions. If the job calls for an EGC that's larger than No. 6 copper or aluminum, it must be color-coded at each end and at every point where the conductor is accessible.

The NEC permits you to use the following methods to identify an EGC larger than No. 6:

• Stripping the insulation or covering from the entire exposed length.

• Coloring the exposed insulation or covering green.

• Marking the exposed insulation or covering with green colored tape or green adhesive labels.

When you're working with a motor circuit, where the OCPD consists of an instantaneous trip circuit breaker or a motor short-circuit protector (as allowed per Sec. 430-52), you must size the EGC based on the rating of the motor overload protective device. In any design, the EGC never has to be larger than the largest ungrounded phase conductor supplying the motor is.

Sometimes you're faced with running circuit conductors in parallel and routing them in separate conduits. In this case, you must run a separate EGC in each conduit. You size the EGC per Table 250-122, based on the rating of the OCPD protecting the circuit [as per Sec. 250-122(f)]. Note that you must install a full size EGC in each conduit. As you can see, the 1999 Code does a nice job of presenting the guidelines for the use of EGCs in a user-friendly format.

Don't miss EC&M Seminar's new Hazardous Location Wiring Conference, presented by James Stallcup, EC&M Contributing Editor and former Chief Electrical Inspector.

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© 2012 Penton Business Media, Inc.

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